Beamforming is a multi-channel array processing method that generates a focused antenna beam electronically, i.e., without the need for physical interaction between a physical aspect of an antenna (such as, for example, a parabolic dish) and an electromagnetic wave. Instead, in antennas comprised of either a linear or a planar two-dimensional array of antenna elements, signals that have been subjected to differing time delays are applied to the antenna elements, thereby focusing the beam formed by the antenna through an electronic process as opposed to a physical process. In essence, a beamformer acts as a spatial band pass filter, amplifying the antenna signal in some directions and attenuating the signal in other directions.
Beamforming, which is inherently a time shift effect, is generally accomplished either through time shift methods or phase shift methods. In time delay beamforming true time delays are applied to signals before they are coupled to antenna elements. In a true time delay beamformer a frequency-independent time delay is added to each channel based on the desired direction of the beam. The phase shift method of beamforming is frequency dependent and approximates the time shift method only over a limited bandwidth.
In contrast to true-time delay beamforming where true time delays are applied to signals, in phase-shift beamforming desired time delays first are converted to phase shifts and then applied to the signals.
In most, if not all, applications, those skilled in the art desire more precise means for controlling beam properties. Signal-to-noise ratios and efficiency of power utilization generally improve with more precise control over beam properties. Those skilled in the art also desire beamforming methods and apparatus that are subject to increased levels of computer control. In analog beamforming equipment components providing time delays require careful matching and tuning for proper operation.
In certain applications, it is desirable to transmit and to receive signals across a relatively wide frequency band. In applications where this is desirable, beamformers using phase shifters are impractical because phase shifters are inherently narrow band devices and are thus incapable of accommodating signals across a wide frequency band.
In other applications, it is desirable to transmit and to receive multiple beams simultaneously. In such applications the limitations of analog-based beamformers associated with size, numbers of interconnections, and complexity of control become even more problematic.
Thus, those skilled in the art desire beamforming methods and apparatus that provide more precise control over beam properties, and are subject to increased levels of computer control.
Those skilled in the art also desire beamforming methods operable over a relatively wide frequency band.
In addition, those skilled in the art desire the ability to form multiple beams simultaneously using the same antenna array.
Further, those skilled in the art desire beamforming methods and apparatus having the ability to form multiple beams simultaneously while maintaining the ability to operate over a relatively wideband frequency range.
Finally, those skilled in the art desire beamforming methods and apparatus that result in relatively small physical implementations.